Method for manufacturing filler container chemical pulp

ABSTRACT

The invention relates to a method for improving the manufacturing and usage economy of a filler, in particular a calcium carbonate based filler, used in the manufacture of paper and board, which calcium carbonate based filler is prepared by precipitating calcium carbonate particles onto the surface of noil fibrils. The invention also relates to a method by means of which it is possible to manufacture and/or produce said filler in a form that can be used directly in paper and board applications. Further, an object of the invention is to provide a method for manufacturing paper and/or board, which method makes use of chemical pulp having said filler incorporated therein as dried in chemical pulp bales.

[0001] The invention relates to a method for manufacturing filler containing chemical pulp, which filler is prepared by precipitating particles comprising an organic or inorganic salt onto the surface of noil fibrils. The invention also relates to a method by means of which it is possible to manufacture and/or produce said filler in a form that can be used directly in paper and board applications. Further, an object of the invention is to provide a method for manufacturing paper and/or board, which method makes use of chemical pulp having said filler incorporated therein as dried in chemical pulp bales. The invention also relates to a method for improving the manufacturing and usage economy of a filler, in particular a calcium carbonate based filler, used in the manufacture of paper and board.

[0002] In recent times, strenuous efforts have been made to develop calcium carbonate based fillers and their manufacturing methods in order to be able to meet the ever-higher quality requirements of high-quality paper, to reduce the loading to the environment and the need of energy, and to improve the runnability of the paper and board machine. Traditionally, in the manufacture of paper and board, a stock is prepared from mechanical pulp or chemical pulp or from a combination of them, and the necessary fillers and other additives can be added to this stock, and further paper or board of desired quality can be manufactured by a suitable method.

[0003] FI patent 100729 discloses a calcium carbonate based filler which gives the paper improved strength properties and a lower basis weight, and by means of which it is generally possible to reduce the costs of paper manufacture. The calcium carbonate based filler is manufactured by precipitating calcium carbonate onto the surface of noil fibrils produced from cellulose fibre and/or mechanical pulp fibre by refining. In that connection, calcium carbonate crystal aggregates are formed that resemble pearl necklaces and are held together by noil fibrils, i.e. fine fibres, and in which the calcium carbonate particles have precipitated onto the noil fibrils, adhering to them. The diameter of the calcium carbonate particles in the aggregates is about 0.2-3 μm. This filler, also known under the trademark SuperFill®, is advantageously based on calcium carbonate and it imparts a clearly improved combination of light-scattering and strengths to the paper as compared with conventional calcium carbonate based fillers. It is particularly significant that the SuperFill® filler is able to impart a very uniform distribution of light-scattering material to the paper.

[0004] The calcium carbonate based SuperFill® filler can be manufactured on an industrial scale mainly as dilute suspensions, which considerably limits the use of the filler. This also leads to the fact that SuperFill® filler can be used only in localities where a plant manufacturing SuperFill® filler is located, because the transport of the filler becomes very uneconomical and difficult because of its high water content. Moreover, if SuperFill® filler is manufactured only in small quantities, manufacturing costs are high, which again leads to the fact that in some product applications the price of the filler becomes too high. Further, the manufacturing process of SuperFill® filler requires special utilities, such as, for example, a sufficiently good source of carbon dioxide, which is not always available in the localities where paper or board is manufactured.

[0005] Based on the above, it may be noted that there exists an obvious need for a method by means of which it is possible to manufacture and/or produce chemical pulp that contains SuperFill® filler, advantageously calcium carbonate based SuperFill® filler, which pulp can be used directly in paper and board applications and by means of which it is possible to avoid or at least substantially reduce the above-mentioned problems of the prior art arrangements.

[0006] An object of the invention is a method by means of which it is possible to manufacture chemical pulp which has SuperFill® filler, advantageously calcium carbonate based SuperFill® filler, incorporated therein in an amount suitable for each paper and board application, as dried and mixed with the chemical pulp, advantageously dried into bales, thereby making it possible to use SuperFill® filler also in manufacturing localities where there is no production plant of said filler.

[0007] An object of the invention is also the thus manufactured chemical pulp which has SuperFill® filler incorporated therein in an amount suitable for each paper and board application.

[0008] An object of the present invention is further a method for improving the manufacturing and usage economy of SuperFill® filler, advantageously calcium carbonate based SuperFill® filler.

[0009] Further, an object of the invention is a method for manufacturing paper and/or board, which method makes use of chemical pulp having SuperFill® filler, advantageously calcium carbonate based SuperFill® filler, incorporated therein as dried in chemical pulp bales.

[0010] The features characteristic of the methods and the chemical pulp according to the invention are set forth in the claims.

[0011] It has been found that the problems associated with the prior art can be substantially reduced or avoided by means of the arrangement in accordance with the invention, wherein SuperFill® filler, advantageously calcium carbonate based SuperFill® filler, which has been prepared by precipitating an organic or inorganic salt, advantageously calcium carbonate, onto the surface of noil fibrils produced by refining from cellulose fibres and/or mechanical pulp fibre, is passed in a dilute suspension to a chemical pulp dryer to be mixed with chemical pulp. In addition to or instead of calcium carbonate, it is also possible to use another light-scattering component precipitated onto the surface of noil fibrils, such as an organic or inorganic salt, of which gypsum, calcium oxalate, barium sulphate, precipitated silicas and silicates may be mentioned as examples. The filler can also contain optionally a dispersing agent, such as, for example, sodium hexametaphosphate.

[0012] In the method in accordance with the invention, the SuperFill® filler is passed in an aqueous suspension, the solids content of which is 0.1-35 wt. %, advantageously 2-6 wt. %, to a chemical pulp dryer and further to be mixed with chemical pulp. After that, the drying of the chemical pulp can be carried out by any method conventionally used for drying chemical pulp. Advanteously, the chemical pulp is dried into bales.

[0013] Optionally, it is also possible to use a separate filler drying line in which SuperFill® filler is dried, recovered and then mixed, at a desired content in a range of 1-70 wt. %, advantageously 1-50 wt. %, with chemical pulp in connection with the manufacture of the chemical pulp before the chemical pulp is dried. After that, the chemical pulp is dried in a conventional manner, advantageously into bales. Drying the filler several times does not substantially reduce its bond potential.

[0014] As a result, chemical pulp, advantageously chemical pulp bales, containing a desired amount of SuperFill® filler uniformly distributed in the chemical pulp, is/are obtained. When needed, the chemical pulp can be refined, but it can also be unrefined.

[0015] Baled chemical pulp containing SuperFill® filler can be pulped in a conventional manner in a paper or board mill, and it can be added to any conventional pulp blend used in the manufacture of paper and board. Paper and board can be manufactured from the SuperFill® filler containing chemical pulp by methods known in themselves, from which methods the conventional separate filler addition phase is now omitted. SuperFill® filler containing chemical pulp can be added to pulp 1-100%.

[0016] In plants manufacturing coating qualities, the differences in the amounts of pigment coming with broke can be compensated for in an appropriate manner, for example, by means of a combination of two chemical pulps having different SuperFill® filler contents.

[0017] The method according to the invention and the thus manufactured chemical pulp have significant advantages over the arrangements of the prior art. The invention makes it possible to substantially improve the profit potential of the technology associated with SuperFill® filler, whereby both the manufacturing economy is improved and the number of application sites is increased. In accordance with the invention, it is possible to manufacture chemical pulp that contains a suitable filler amount for each paper and board application. The method makes it possible to avoid transporting large amounts of water, thereby saving energy, costs and spaces. The thus manufactured SuperFill® filler containing chemical pulp can be transported even long distances and it can also be used in manufacturing localities and in product applications which lack the utilities necessary for building a PCC plant, such as, for example, a sufficient source of carbon dioxide or suitable pulp processing devices. By this means it is also possible to manufacture chemical pulp of uniform quality containing a precisely predetermined amount of SuperFill® filler. It is possible to manufacture paper and board of more uniform quality, the properties of which are superior to those of the paper manufactured in a conventional manner.

[0018] The invention makes a centralized SuperFill® filler production plant possible, which has a high capacity and which is capable of manufacturing filler at lower costs. The production plant may optionally also comprise a separate drying line for the filler.

[0019] The method in accordance with the invention is illustrated by means of the following examples, but the invention is not meant to be limited to them.

EXAMPLE 1

[0020] Manufacture of SuperFill® filler containing chemical pulp

[0021] a) A SuperFill® filler suspension was prepared by a known method which is described, among other things, in FI patent 100729.

[0022] b) SuperFill® filler containing chemical pulp was manufactured by passing 625 kg, calculated as solids, of the SuperFill® filler suspension manufactured in point a) and containing 500 kg of CaCo₃ and 125 kg of noil fibrils, so as to be mixed with chemical pulp (375 kg of unrefined or slightly refined birch pulp), which was then dried in a conventional manner, and 1000 kg of SuperFill® filler containing chemical pulp was obtained, calculated as solids.

EXAMPLE 2

[0023] Use of SuperFill® filler containing chemical pulp in the manufacture of paper

[0024] Paper was manufactured from the SuperFill® filler containing chemical pulp described in Example 1 in a conventional manner on a paper machine such that 1 ton of paper contained:

[0025] 600 kg SuperFill® filler containing chemical pulp which contained

[0026] 300 kg CaCo₃

[0027] 225 kg birch pulp

[0028] 75 kg noil fibrils

[0029] 250 kg birch pulp

[0030] 150 kg softwood pulp

[0031] in total 1000 kg

[0032] SuperFill® filler containing chemical pulp was added to the stock in the manufacture of paper such that the paper contained 30 wt. % of CaCO₃ and, of the chemical pulp in the paper, 76 wt. % was birch pulp and 24 wt. % was softwood pulp. The opacity, brightness, smoothness and formation of the thus manufactured paper were superior to those of the corresponding paper which was manufactured in a traditional manner and to which filler was added separately. Moreover, the runnability of the paper machine remained unchanged. 

1. A method for manufacturing filler containing chemical pulp, characterized in that the filler is prepared by precipitating a light-scattering organic or inorganic salt onto the surface of noil fibrils produced by refining from cellulose fibres and/or mechanical pulp fibre, and the thus prepared filler is passed in an aqueous suspension to a chemical pulp dryer to be mixed with chemical pulp and the chemical pulp is dried or said filler is dried, mixed with chemical pulp before the chemical pulp is dried, and the chemical pulp is dried.
 2. A method as claimed in claim 1, characterized in that the chemical pulp is dried into bales.
 3. A method as claimed in claim 1 or 2, characterized in that the light-scattering organic or inorganic salt is calcium carbonate, gypsum, calcium oxalate, barium sulphate, precipitated silica or silicate, or a combination thereof.
 4. A method as claimed in claim 1, characterized in that the light-scattering organic or inorganic salt is calcium carbonate.
 5. A method as claimed in claim 1, characterized in that the solids content of the filler in the suspension is 0.1-35 wt. % and, when dried filler is mixed with chemical pulp, the amount of the filler is 1-70 wt.
 6. A method as claimed in claim 5, characterized in that the filler content in the suspension is 2-6 wt. %.
 7. A method as claimed in claim 1, characterized in that the chemical pulp has been refined.
 8. A method as claimed in claim 1, characterized in that the filler contains a dispersing agent.
 9. A method for manufacturing paper or board, characterized in that filler containing chemical pulp or a combination of filler containing chemical pulps manufactured by the method as claimed in claim 1 is added to a stock blend which is used in the manufacture of paper or board and from which paper or board is made.
 10. A method as claimed in claim 9, characterized in that filler containing chemical pulp or a combination of filler containing chemical pulps is pulped and added to a stock blend which is used in the manufacture of paper or board and from which paper or board is made.
 11. The use of filler containing chemical pulp or a combination of filler containing chemical pulps manufactured by the method as claimed in claim 1 in the manufacture of paper or board. 